1. Field of the Invention
The present invention relates to a push-pull control cable for transmitting an operation effort in pushing and pulling directions.
2. Description of the Prior Art
In Japanese Patent Laid-open Publication No. 7(1995)26646, there has been proposed a push-pull type control cable including an inner cable comprised of a plurality of strands each formed by more than five pieces of twisted element wires and wound around a core wire, the inner cable being inserted into a conduit tube to be displaced in an axial direction for transmitting an operation effort applied to its one end at a push-side or a pull-side. In use of the control cable, lubricant is filled in a clearance between the inner periphery of the conduit tube and the outer periphery of the inner cable to reduce friction of the inner cable in the conduit tube thereby to enhance load efficiency and durability of the control cable. In the conventional control cable, however, a sufficient amount of lubricant may not be filled in the clearance between the inner cable and the conduit tube. As a result, the enhanced load efficiency and durability of the control cable may not be maintained for a long period of time.
An object of the present invention is to provide a push-pull type control cable the load efficiency and durability of which are maintained in an enhanced condition for a long period of time.
According to the present invention, the object is accomplished by providing a push-pull type control cable having a conduit tube and an inner cable comprised of a core wire and a plurality of strands wound around the core wire and inserted into the conduit tube, the control cable being filled with lubricant at a clearance between an inner periphery of the conduit tube and an outer periphery of the inner cable, wherein the plurality of strands each are comprised of three pieces of element wires twisted in a manner of ordinary lay (twisted in a reverse direction relative to the winding direction of the strands. In the push-pull type control cable, a sufficient amount of lubricant is filled in a clearance between the outer periphery of the inner cable and the inner periphery of the conduit tube since rugged surfaces larger in roughness are formed on the strands of the inner cable. This is useful to maintain load efficiency and durability of the control cable in an enhanced condition for a long period of time. As the element wires each are relatively large in diameter to enhance each bending stiffness of the strands in a small diameter, the buckling strength of the inner cable can be increased to enhance operability of the control cable. As the outer peripheral area of the inner cable in contact with the inner periphery of the conduit tube is reduced, friction of the inner cable caused by displacement in the conduit tube can be decreased to enhance the load efficiency of the control cable. In addition, the three pieces of element wires of each strand are twisted in such a manner that each element wire is pressed into contact with other two element wires to maintain the configuration of each strand for a long period of time.
In actual practices of the present invention, it is desirable that the plurality of strands each are comprised of three pieces of element wires twisted in a manner of ordinary lay (twisted in a reverse direction relative to the winding direction of the strands around the core wire). In the strands of the inner cable, the element wires are stranded at a small angle relative to the axial direction of the inner cable to enhance the buckling strength of the inner cable. As the element wires appeared on the inner cable are aligned in parallel in the axial direction of the inner cable, the friction of the inner cable caused by displacement in the conduit tube is reduced to enhance the load efficiency and durability of the control cable.
In actual practices of the present invention, the plurality of strands may be provided in the form of a plurality of first strands each comprised of twisted element wires of large diameter twisted in a manner of ordinary lay (twisted in a reverse direction relative to the winding direction of the first strands and a plurality of second strands comprised of element wires of small diameter twisted in the same manner as in the first strands, wherein the first and second strands are alternately wound around the core wire. With such an arrangement, a sufficient amount of lubricant can be filled in a clearance between the second strands and the inner periphery of the conduit tube to maintain the load efficiency and durability of the control cable in an enhanced condition for a long period of time. In addition, the load efficiency of the control cable is further enhanced as the outer peripheral area of the inner cable in contact with the inner periphery of the conduit tube is reduced.
In actual practices of the present invention, the plurality of strands may be provided in the form of a plurality of first strands each comprised of three pieces of element wires twisted in a manner of ordinary lay and a plurality of second strands each comprised of three pieces of element wires twisted in a manner of langs lay (twisted in the same direction as the winding direction of the strands on the core wire), wherein the first and second strands are alternately wound around the core wire. With this arrangement, the operability, load efficiency and durability of the control cable can be enhanced, and the elasticity of the inner cable can be enhanced since the angle of the element wires relative to the axis line of the inner cable is increased.
In the above arrangement, the first strands each may be comprised of stranded element wires of large diameter, while the second strands each may be comprised of twisted element wires of small diameter. With this arrangement, a sufficient amount of lubricant can be filled to maintain the load efficiency and durability of the control cable in an enhanced condition for a long period of time. In this case, the friction caused by axial displacement of the inner cable in the conduit tube is reduced since only the first strands formed in the ordinary lay are in contact with the inner periphery of the conduit tube. This serves to enhance the elasticity of the control cable without causing deterioration of the load efficiency and durability.
Furthermore, the push-pull type control cable may be provided in the form of a control cable having an inner cable comprised of a strand formed by three pieces of twisted element wires and a single wire of small diameter alternately wound around a core wire and inserted into a conduit tube, the control cable filled with lubricant at a clearance between an inner periphery of the conduit tube and an outer periphery of the inner cable.